This invention relates to the computer-implemented processing of operations performed on digital images from source to destination having different pixel aspect ratios.
Programmed computers can be used to edit and create images and movies. For example, a computer program product called After Effects, available from Adobe Systems Incorporated of Mountain View, Calif., is licensed for used on a variety of personal computers and provides its user the ability to edit and create movies by integrating and arranging images and pieces of footage. The images in such systems are digital (discrete) arrays of values, each value associated with a picture element (pixel). A pixel may be addressed as a point in a space, typically a planar surface of two dimensions. However, when displayed on a display monitor or produced on an output device, a pixel covers an area and has a horizontal and vertical dimension. For the purposes of this specification, a pixel may be thought of as having rectangular dimensions (which includes the square as a special case). A grid of pixels defines a graphical frame of predetermined dimensions. For example, the D1 NTSC video standard employs a frame of 720.times.486 pixels.
The ratio of the dimensions of the frame defines a "frame aspect ratio". Similarly, the ratio of the dimensions of the pixels composing the frame defines a "pixel aspect ratio". The pixel aspect ratio of a square pixel is one, and it is said to have a "square pixel aspect ratio". Standard computer video display monitors have a frame aspect ratio of 4:3 (width to height) and square pixels.
If the pixels are not square, the pixels are said to have a "nonsquare pixel aspect ratio". D1 NTSC video, for example, does not have a 4:3 frame aspect ratio and has pixels that are taller than they are wide. D1 PAL pixels, on the other hand, are wider than they are tall. The present invention will find application whatever the nature of the differences in pixel aspect ratio.